Internal combustion engines exhaust a mixture of air pollutants, which may be composed of gaseous compounds, as well as solid particulate matter. One byproduct of fuel combustion in an internal combustion engine is carbon particles, which are typically referred to as soot. Due to regulated emission standards, engine manufacturers have employed various components and systems to control and limit the amount of soot emitted into the environment.
One such device that has been commonly used to collect soot, ash, and other particulate matter before entering the environment is a diesel particulate filter. However, extended use of diesel particulate filters may cause matter to build up in the filters and reduce their functionality, as well as engine performance. Soot may be burned off through a regeneration process, but the ash, which is generally a non-combustible by-product of lubricating oils, cannot be reduced and therefore accumulates in the diesel particulate filter. The ash must either be removed by cleaning the filter to remove the ash on a periodic basis to restore exhaust flow through the filter, or the diesel particulate filter must be replaced.
Cleaning tools may be used for removing ash from diesel particulate filters. However, engineers continue to search for a way to check the cleanliness of the diesel particulate filter and effectiveness of the cleaning process before re-installation of the diesel particulate filter into the engine. Conventionally, measurements of backpressure through the filter, before and after cleaning, have been used to derive the cleanliness of the filter, but have not consistently yielded accurate results. This is because the change in flow resistance due to ash accumulation is so small that it is difficult to measure a change in pressure unless the air flow generated to develop the pressure is extremely high, which would require large and expensive blower hardware. Alternatively, boroscope equipment may be used to determine the ash column height in a channel of a diesel particulate filter by directly viewing the ash height in individual filter columns; however, use of this type of equipment is expensive and time consuming.
Thus, there exists a need for an improved, reliable, and cost-effective apparatus and method for determining ash height in a filter.